This invention relates to improvements in a nozzle to be used for hydrostatic forming, for example, of a frame of an automotive vehicle, and to a hydrostatic forming system using such a nozzle.
Hitherto a frame and the like of an automotive vehicle have been produced mainly by a hydrostatic forming system or apparatus. The hydrostatic forming system usually includes upper and lower dies mounted on a base, and hydrostatic forming nozzles secured to hydraulic cylinders. In hydrostatic forming with such a hydrostatic forming system, the tip end sections of the hydrostatic forming nozzles are respectively inserted into the opposite end sections of a tube (raw material) located between the upper and lower dies, under pressure of the hydraulic cylinders. Then, pressurized fluid is supplied through the nozzles into the tube, so that the tube is formed into a desired formed product.
However, difficulties have been encountered in the above earlier technique. That is, since each hydrostatic forming nozzle has usually a circular cross-section, the formed product or semi-product after the hydrostatic forming has a surplus section in addition to a product section corresponding to an actual product such as the automotive vehicle frame. The surplus section is a section into which the nozzle has been fitted. The actual product has, in general, a non-circular cross-section such as a rectangular cross-section, and therefore the above surplus section is unnecessary for the actual product. As a result, it is required to remove the surplus section, so that the surplus section is useless. This is not desirable to lower a production cost for the actual product.